Everyone who lives in a northern climate knows the hazards of driving on icy roads. No matter how experienced you are at navigating them, you can still end up in the ditch. This is why every time there is bad weather, you are going to find the city trucks out there trying to make the conditions better. One thing the city might put on the roads is sand to provide a little extra traction. But to really help the road situations, they pour salt on it. Why? Because salt melts ice and pouring it on the roads is one of the best ways to clear the ice off.
Why Does Salt Melt Ice
In wintry conditions, ice will form when the temperature reaches 32 degrees Fahrenheit (or 0 degrees Celsius). By adding salt, you are lowering the freezing and melting point of water. When you add salt to water (or in this case, ice) you are introducing dissolved particles. As more particles are added and dissolved, the freezing point of water gets lower.
However, these results are in an ideal environment. In real world terms, on roads and sidewalks during the winter, salt can only lower the freezing point to around 15 degrees Fahrenheit. So if the temperature is lower than 15 degrees, the better option is to sprinkle sand on the roads because the ice won’t be able to melt it.
Since we are on the subject, I should mention another use for combining salt with ice. Besides melting the ice, salt is also used to make it colder. This is why salt is used in making homemade ice cream the old fashioned way. The ice cream mixture is in a metal canister than spins inside a container. The container is filled with ice water. But in order for the ice cream to freeze, it has to reach a temperature below 32 degrees. By mixing salt into the ice water surrounding the canister, you lower the melting temperature of the ice to around 0 degrees Fahrenheit. This creates a very cold brine that easily freezes the ice cream.
Which Salts Are Used To Melt Ice
So which salts are used to melt ice? There are four primary salts and they all have different properties. The most common used to deice roads is rock salt, or sodium chloride. It works well on roads as long as the temperature is above 15 degrees Fahrenheit. The problem with rock salt is that it releases chloride ions as it melts. These ions can be hazardous to plants, streams, and other water sources. They also corrode metal so rock salt on the roads is hard on cars.
Another salt for melting ice is calcium chloride. These look like small white pellets. This type of salt can melt ice if the temperature reaches 0 degrees Fahrenheit. The drawbacks to calcium chloride are that it can irritate your skin and can cause damage and corrosion to concrete so it is not the best to use on sidewalks.
Potassium chloride is an excellent de-icer for roads and sidewalks. It can melt ice at temperatures above 15 degrees but there are chemical additives that you can use with it that allow it to melt at lower temperatures. Unlike calcium chloride, potassium chloride is safe to handle and will not pollute waters or harm vegetation.
Finally, the latest type of salt that is used to melt ice is magnesium chloride. This salt will melt ice even when the temperature reaches -13 degrees Fahrenheit. It is also safer for the environment because it releases the lowest amount of chloride ions. It will not irritate your skin or cause damage to concrete. Plus, you can walk on it and not leave tracks of it through your home.